I assumed my husband had already checked with our guests that they liked fish - he had not.

And, as the guests arrived, we were informed that not only was one of them allergic to it, but that they should not be too close to anyone else eating it.

A thorough clean of the kitchen and straight to the main course.

Allergies

No harm done, but it could have been a different story.

Adverse reactions to foods affect between 3% and 6% of the population and can range from a mild rash and feelings of nausea to anaphylaxis, which can kill due to obstructed breathing.

Most people are aware of peanut allergies, but how many know that you can be allergic to a carrot or its entire family

Professor Adrian Newland

An allergy is an exaggerated immune response against substances that can by themselves be quite harmless.

The body reacts to these triggers, called 'allergens', releasing chemicals which make the tissues swollen, red, itchy and irritable.

Awareness about allergy to foods like peanuts is good, but there are more unusual allergies.

Visitors to the Chelsea Flower Show, which opens on Wednesday, will be able to see an exhibition by the Royal College of Pathologists entitled "The pathology of plant sensitivities", which looks in particular at allergies to plants.

Peanuts are a well known allergen

Professor Adrian Newland, president of the Royal College of Pathologists, explained that the flower show was a good opportunity for pathologists to explain an important part of their work.

"We have been doing these stands at the Chelsea Flower Show for a number of years, each with a different theme," he said.

"There is an element of education about them, but also to get people to think about what pathologists do.

"People have an image of pathologists from TV shows where they are concerned with dead bodies. We are a much broader church than people would believe.

"Most people are aware of peanut allergies, but how many know that you can be allergic to a carrot or its entire family?"

Plant family

Prof Newland said that those allergic to carrots, for example, could also have reactions to the rest of the carrot family - parsley, coriander, parsnip, celery, fennel, dill and anise.

Those allergic to pumpkin can have reactions to cucumber, squash courgettes and watermelon. And people allergic to sunflowers can also react to honey.

Dr Joanne Sheldon, an immunologist based at St. George's Hospital, London, explained why an entire plant family could cause a similar allergic response - cross-reactivity.

Plants comprise a complex mixture of components and some are common to a number of plants.

For example, people with pollen allergy 'hay fever' may sometimes get similar symptoms - sneezing, runny nose, or asthma - when they eat apples, plums, cherries or peaches, as they contain similar allergens.

And wheat - the second most common cereal grain in the world - had been shown to be linked to coeliac disease as the gluten it contains causes an immune reaction in the gut wall.

Display

Dr Sheldon said that, as well as alerting and informing visitors about the various allergens, the pathologists would be on hand to offer advice and information about where to go for testing.

She said they expected a good turn out. "I think people are interested in plants. Last year when we had an exhibition at the flower show we had 7,000 visitors to our stand."

Visitors will be able to see plants

The exhibition also includes a hands-on section where visitors can view microscopic slides of a 'normal' gut and one with a digestive disorder called coeliac disease, see plants such as apples and carrots growing, peanuts in flower and in 'fruit', wheat and herbs.

Dr Tim Wreghitt, a microbiologist based at Addenbrookes, Cambridge, said he hoped the public would gain valuable information about what they are eating.

"Most people understand that certain trigger-foods such as wheat, soy, peanuts and fruit can sometimes cause adverse reactions, but in fact every food has the potential to cause a problem."